An area man with a history of violent crimes will be sentenced to 8 1/2 years in prison in December for stabbing a man during a drug transaction in New London and threatening employees of a Groton doctor’s office with a hammer.

Justin C. “Moo” Henderson, 33, most recently of Mystic, pleaded guilty Monday in New London Superior Court to first-degree robbery and second-degree threatening. He entered his plea under the Alford Doctrine, indicating he does not agree with the state’s version of events but does not want to risk a harsher sentence if convicted at trial.

According to court documents and testimony, Henderson stabbed Jonathan Smith in a stairwell at Smith’s apartment at 70 Farmington Ave. in New London after going to the apartment to purchase marijuana on March 27, 2014. Prosecutor David J. Smith (no relation) said police recovered video showing Henderson chasing the victim with a knife. Jonathan Smith was treated for stab wounds to the chest, torso and legs and slicing injuries to his fingers.

On Feb. 14, 2014, Henderson went to a medical office on Gold Star Highway and threatened employees with a hammer, causing them to fear for their lives, according to the prosecutor. Employees reported that Henderson, who had received a massage at the office, kept leaving and returning and was acting peculiar. At one point, they said, he entered the room of a massage therapist, raised the hammer over her head and swung it at her. She was not hurt, but Henderson used the hammer to threaten another employee who went toward the office after hearing the massage therapist’s screams.

Henderson, represented by attorney Anthony Basilica, was found competent to stand trial following an evaluation in October 2014. According to a report by the clinical team that evaluated him, his “drug of choice” is PCP and he has been smoking two to three marijuana blunts every day since his early teens.

He has previous convictions for carrying a pistol without a permit, attempted robbery, possession of narcotics and interfering with police, according to Judicial Branch records.

Judge Hillary B. Strackbein will be sentencing Henderson on Dec. 14 to 8 1/2 years in prison followed by six years of special parole.

k.florin@theday.com

Twitter: @KFLORIN